Method for calculating spatial and temporal distribution of the Gutenberg-Richter parameter for induced subsurface seismic events and its application to evaluation of subsurface formations

Abstract

A method for evaluating fractures induced in subsurface formations includes determining hypocenters and origin times of induced seismic events from seismic signals detected by seismic sensors deployed above a volume of the subsurface formations to be evaluated and recording the detected signals for a selected time. A modified Gutenberg-Richter exponent is determined for each induced seismic event having at least a selected number of other induced seismic events within a selected radial distance thereof. A spatial distribution of the modified Gutenberg-Richter exponents is used to determine at least one property of the induced fractures.

What is claimed is: 
     
       1. A method for evaluating fractures induced in subsurface formations, comprising:
 determining hypocenters and origin times of induced seismic events from seismic signals detected by seismic sensors deployed above a volume of the subsurface formations to be evaluated and recording the detected signals for a selected time; 
 determining, using a computer, a modified Gutenberg-Richter exponent for each induced seismic event having at least a selected number of other induced seismic events within a selected radial distance thereof; 
 using a spatial distribution of the modified Gutenberg-Richter exponents to determine at least one property of the induced fractures. 
 
     
     
       2. The method of  claim 1  wherein the at least one property comprises identification of whether an induced seismic event is caused by reactivation of an existing fault or creation of a new fault. 
     
     
       3. The method of  claim 1  wherein the at least one property comprises identification of whether an induced seismic event is a result of a tectonic fault or an induced fault. 
     
     
       4. The method of  claim 1  wherein determining the modified Gutenberg-Richter exponent for each induced seismic event comprises:
 identifying a smallest magnitude one of the induced seismic events; 
 calculating an arithmetic mean of magnitudes of all induced seismic events within the selected radial distance; and 
 using the smallest magnitude and arithmetic mean to determine the modified Gutenberg-Richter exponent. 
 
     
     
       5. The method of  claim 1  wherein determining the modified Gutenberg-Richter exponent for each induced seismic event comprises:
 identifying a smallest magnitude one of the induced seismic events; 
 calculating an arithmetic mean of magnitudes of all induced seismic events within the selected radial distance and closest in time of occurrence to the induced seismic event being evaluated; and 
 using the smallest magnitude and arithmetic mean to determine the modified Gutenberg-Richter exponent. 
 
     
     
       6. The method of  claim 1  wherein the induced seismic events are generated by pumping a fracture treatment into a wellbore drilled through selected subsurface formations. 
     
     
       7. A computer readable medium having stored thereon a computer program, the program having logic operable to cause programmable computer to perform a method for evaluating fractures induced in subsurface formations, the method including steps comprising:
 determining hypocenters and origin times of induced seismic events from seismic signals detected by seismic sensors deployed above a volume of the subsurface formations to be evaluated and recording the detected signals for a selected time; 
 determining a modified Gutenberg-Richter exponent for each induced seismic event having at least a selected number of other induced seismic events within a selected radial distance thereof; 
 using a spatial distribution of the modified Gutenberg-Richter exponents to determine at least one property of the induced fractures. 
 
     
     
       8. The computer readable medium of  claim 7  wherein the at least one property comprises identification of whether an induced seismic event is caused by reactivation of an existing fault or creation of a new fault. 
     
     
       9. The computer readable medium of  claim 7  wherein the at least one property comprises identification of whether an induced seismic event is a result of a tectonic fault or an induced fault. 
     
     
       10. The computer readable medium of  claim 7  wherein determining the modified Gutenberg-Richter exponent for each induced seismic event comprises:
 identifying a smallest magnitude one of the induced seismic events; 
 calculating an arithmetic mean of magnitudes of all induced seismic events within the selected radial distance; and 
 using the smallest magnitude and arithmetic mean to determine the modified Gutenberg-Richter exponent. 
 
     
     
       11. The computer readable medium of  claim 7  wherein the determining he modified Gutenberg-Richter exponent for each induced seismic event comprises:
 identifying a smallest magnitude one of the induced seismic events; 
 calculating an arithmetic mean of magnitudes of all induced seismic events within the selected radial distance and closest in time of occurrence to the induced seismic event being evaluated; and 
 using the smallest magnitude and arithmetic mean to determine the modified Gutenberg-Richter exponent. 
 
     
     
       12. The computer readable medium of  claim 7  wherein the induced seismic events are generated by pumping a fracture treatment into a wellbore drilled through selected subsurface formations.